1. Field of the Invention
The present invention relates to improvements in an oil pan for an automotive vehicle, and more particularly to the oil pan in which the oil dropped on the oil pan is rapidly returned into a sump.
2. Description of the Prior Art
It is well known that an internal combustion engine is provided with an oil pan having a sump into which lubrication oil dropped in the oil pan is collected to be fed to various sections of the engine by an oil pump In order to effectively return the lubrication oil into the sump, it has been proposed that an oil pan has a plurality of guide ribs on a shallow bottom section of the oil pan as shown in the FIGS. 15 and 16 of the present application. Such an arrangement is disclosed, for example, in Japanese Patent Publication No. 53-16048.
As shown in FIGS. 15 and 16, an oil pan 51 includes a sump 52 which is disposed under a cylinder block and extends along the axis of a crankshaft 54. A shallow bottom section 53 of the oil pan 51 is disposed under the cylinder block and defines a space which is communicated with the sump 52. An oil strainer (not shown) is disposed in the sump 52. A generally straight rib 57 is formed at the upper surface of one side of the shallow bottom section 53 which is located downstream of the oil flow caused by the rotation of the crankshaft 54. The straight rib 57 extends generally in the longitudinal direction of the engine 50. A plurality of arcuate ribs 56 are formed at the upper surface on the other side of the shallow bottom section 53 which is located upstream of the oil flow caused by the rotation of the crankshaft 54. Lubrication oil in the shallow bottom section 53 is collected under the rotation of the crankshaft. This causes lubrication oil to be rapidly returned from the shallow bottom section 53 into the sump 52. The shallow bottom section 53 is located considerably near the crankshaft since modern engines have become formed smaller
However, with this conventional arrangement, lubrication oil guided by the ribs 56 flows into the sump 52 through a flat section 59 which is formed between the straight rib 57 and the end 56a of the each arcuate rib 56. Additionally, since the width of the flat section 59 gradually becomes narrow in the direction of the sump 52 while the amount of the oil directed to the sump 52 is increased on the flat section 59 with approaching to the sump 52, the oil on the flat section 59 overflows the ribs 56 and 57 in the vicinity of the sump 52 and is splashed by the air flow force caused by the high speed rotation of the crankshaft 54 and the connecting rods, so that the oil is prevented from returning into the sump 52. Furthermore, since the flat section 59 is located just under the crankshaft 54 to have a short distance relative to the crankshaft 54 and the connecting rods, the oil on the flat section 59 strongly receives the air flow force caused by the high speed rotation of the crankshaft 54 and the like, so that the oil is further prevented from returning into the sump 52.
Therefore, the oil tends to be splashed by the crankshaft 54 and connecting rods 55. This causes the problems that the oil amount lacks in the sump 52, and therefore air is sucked into an oil flowing circuit through the oil strainer. Thus, a large amount of air bubbles is mixed with the oil.